The present invention relates generally to scroll type compressors and more specifically to scroll type compressors incorporating a fluid brake operative to resist and impede reverse movement of the orbiting scroll member.
Scroll type machines are becoming more and more popular for use as compressors in both refrigeration as well as air conditioning applications due primarily to their capability for extremely efficient operation. Generally, these machines incorporate a pair of intermeshed spiral wraps, one of which is caused to orbit relative to the other so as to define one or more moving chambers which progressively decrease in size as they travel from an outer suction port toward a center discharge port. An electric motor is provided which operates to drive the orbiting scroll member via a suitable drive shaft affixed to the motor rotor. In a hermetic compressor, the bottom of the hermetic shell normally contains an oil sump for lubricating and cooling purposes.
Because scroll compressors depend upon a seal created between opposed flank surfaces of the wraps to define successive chambers for compression, suction and discharge valves are generally not required. However, when such compressors are shut down, either intentionally as a result of the demand being satisfied or unintentionally as a result of a power interruption or other problem, there is a strong tendency for the gas in the pressurized chambers and/or backflow of compressed gas from the discharge chamber to effect a reverse orbital movement of the orbiting scroll member and associated drive shaft. This reverse movement often generates objectionable noise or rumble. Further, in machines employing a single phase drive motor, it is possible for the compressor to begin running in the reverse direction should a momentary power failure be experienced. This reverse operation may result in overheating of the compressor and/or other damage to the apparatus. Additionally, in some situations, such as a blocked condenser fan, it is possible for the discharge pressure to increase sufficiently to stall the drive motor and effect a reverse rotation thereof. As the orbiting scroll rotates in the reverse direction, the discharge pressure will decrease to a point where the motor again is able to overcome this pressure head and rotate the scroll member in the "forward" direction. However, the discharge pressure will now increase to a point where the cycle is repeated. Such cycling may also result in damage to the compressor and/or associated apparatus.
The present invention overcomes these problems by incorporating one-way drive means, such as a one-way clutch, coupled between the drive shaft and a paddle disposed in the compressor oil sump. When the drive shaft is rotating in the desired direction the clutch is inoperative to drive the paddle, but when rotation reverses, the drive shaft rotates the paddle in the sump so that it acts like a fluid brake to resist and impede movement of the orbiting scroll member in a reverse direction, thereby eliminating the objectionable noise generated upon shut down of the compressor. Further, this fluid brake operates to resist damage to the motor and/or compressor resulting from a reversing of single phase motors as well as resisting the cyclical reversing resulting from a blocked or failed condenser fan. The brake is passive in that it does not create any load during normal operation of the compressor.
The present invention is an improvement over the concept disclosed in U.S. Pat. No. 4,998,864, the disclosure of which is hereby incorporated herein by reference, wherein the drive shaft is connected to a rigid structure by a one-way clutch to prevent reverse rotation. Braking with the present design is much gentler, thereby significantly increasing the life of the one-way clutch mechanism.
Several embodiments of the novel anti-reverse rotation mechanism are shown including a two bladed paddle, a three bladed paddle and two versions of two piece paddles. The two and three bladed paddles impart angular momentum into the lubricating oil as they attempt to displace the oil. The two piece designs of paddles provide a rotating paddle to impart angular momentum to the lubricating oil and a stationary housing which resists the movement or displacement of the lubricating oil. The resistance offered by the stationary housing provides a higher dampening of the reverse rotation. In addition, there are illustrated versions of the apparatus which also incorporate an integral circular rotor shield of the type generally disclosed in U.S. Pat. No. 5,064,356, the disclosure of which is hereby incorporated herein by reference. Such a shield is useful in reducing the oil level in the area surrounding the rotating motor rotor during operation. In order to insure that sufficient lubricating oil is contained within the sump to assure adequate lubrication and/or cooling of the moving parts while also minimizing the overall height of the housing, it is sometimes necessary that the oil level extend above the rotating lower end of the rotor. However, the relatively high viscosity of the oil as compared to refrigerant gas creates an increased drag on rotation of the rotor resulting in increased power consumption. This problem is further aggravated in scroll compressors because they typically employ a counterweight secured to the lower end of the rotor. The present shield incorporates a generally flat circular disk or flange positioned in close proximity to the lower end of the rotor which serves to reduce return flow of oil to the area of the rotating rotor and/or counterweight but still enables some circulation thereof, which thereby increases the circulation of oil across the adjacent motor stator end turns. In operation, it has been found that this improved shield has resulted in improved cooling of the stator end turns without any substantial effect on the overall operating efficiency of the compressor.
Additional advantages and features of the present invention will become apparent from the subsequent description and the appended claims taken in conjunction with the accompanying drawings.